The invention relates to a machine for wrapping commodities of substantially parallelepiped shape, and in particular, a machine serving to envelop such parallelepiped items in an outer wrapping of transparent material.
The prior art embraces machines for placing an outer wrapping around parallelepiped commodities, especially packs of cigarettes (the case to which the following specification refers); such machines comprise a head, or wheel, rotatable intermittently about a horizontal axis and affording peripheral radial pockets spaced apart one from the next at identical angular distances, each of which designed to accommodate one pack.
The single pocket comprises a bottom wall, nearest the center of the wheel, two substantially radial walls set apart one from the other at a distance essentially matching that of the thickness of one pack, and two end walls embodied generally as two blades lying in planes normal to the axis of the wheel, one on either side, separated by a distance corresponding substantially to the longitudinal dimension of the finished pack.
During each pause produced by intermittent rotation of the wheel, one of the pockets comes to rest at an entry station, in alignment with a reciprocating push rod; stroking forward, the rod engages one pack of cigarettes from the rear flank (considered in relation to the path of entry) and directs it into the waiting pocket together with the wrapper, which consists in a single sheet of material fed through a vertical plane transversely to the path of the entering pack.
On completion of the push rod stroke, the pack will be fully inserted in the pocket with its leading flank flush against the bottom wall.
During the course of this operation, the wrapper is folded gradually into a U shape around the pack, enveloping it on three sides.
The transverse dimension of the wrapper, as seen in relation to the direction of entry, is such that its two sides project a given distance beyond the longitudinal dimension of the pack.
On insertion of the pack into the pocket, these projections will be engaged by the leading edges of the blades aforementioned, and folded in part to envelop a proportion of the two faces of the pack normal to the wheel, i.e. the end faces.
Likewise, the longitudinal dimension of the wrapper is such that, when folded into the `U` formation, the relative ends project beyond the peripheral limit established by the two radial walls of the pocket.
These two projecting ends, or flaps, are folded subsequently, the one by a moving element made to stroke across the entry point, and the other by a fixed element forming part of a cowling coaxial with the wheel, which engages the relative part of the wrapper as the wheel is set in rotation. With the two radial flaps folded and overlapping, and the wrapper enveloping the pack essentially in tubular fashion, the flank of the pack outermost is offered to a heat-seal device located at a further station subsequently to be occupied by the indexing pocket, and the flaps are fused together.
With the pack enveloped thus far by the transparent wrapper and entirely encompassed by the wheel and cowling with the exception of its top and bottom ends, the pocket is indexed ultimately to an exit station diametrically opposed to the entry station, where a further reciprocating push rod proceeds to eject the pack from the wheel, directing it forward into a runout channel along which the operations of folding and sealing the ends of the wrapper will be brought to completion.
It has been found that, when operating speeds are stretched beyond certain limits, wrapping machines of the type in question begin to betray drawbacks that lead to a decided deterioration in quality of the wrapping.
Beyond such operating speed limits, in effect, the centrifugal force and acceleration produced by the indexing movement of the wheel can cause the pack to shift uncontrollably within the relative pocket, resulting in loss of the correct position of the wrapping as it folds around the pack.
It has been observed in particular, that with the pack thrusting against the two overlapping radial flaps folded along its outermost flank, the tubular formation of the wrapping is disturbed.
The ultimate consequence of such movement is that wrappings become substandard, especially from the standpoint of appearance, and instead of hugging the pack closely, are spoilt by creases and kinks, and corners that fail to coincide with the corners of the pack.
The object of the present invention is to embody a wrapping machine in which all the defects of prior art machines as described above can be overcome, in short, a machine capable of enveloping commodities faultessly in close-fitting wrappings even at ultra high operating speeds.